Case-control study of 24 hour ambulatory blood pressure in patients with obstructive sleep apnoea and normal matched control subjects

Background-There is considerable debate regarding the relationship between obstructive sleep apnoea (OSA) and hypertension. It is unclear whether OSA is an independent vascular risk factor as studies attempting to assess this association have produced conflicting results because of confounding varia bles such as upper body obesity, alcohol, and smoking. A case-control study of 24 hour ambulatory blood pressure was undertaken in patients with OSA a nd matched controls to assess whether OSA is an independent correlate of di urnal hypertension. Methods-Forty five patients with moderate to severe OSA and excessive dayti me sleepiness were matched with 45 controls without OSA in a sleep study. M atched variables included age, body mass index (BMI), alcohol, cigarette us age, treated hypertension, and ischaemic heart disease. Upper body obesity was compared by waist:hip and waist:height ratios; 24 hour ambulatory blood pressure recordings were performed (before treatment for OSA) in all subje cts. Results-Patients with OSA had significantly increased mean (SD) diastolic b lood pressure (mm Hg) during both daytime (87.4 (10.2) versus 82.8 (9.1); p =0.03, mean difference 4.6 (95% CI 0.7 to 8.6) and night time (78.6 (9.3) v ersus 71.4 (8.0); p<0.001, mean difference 7.2 (95% CI 3.7 to 10.6)), and h igher systolic blood pressure at night (119.4 (20.7) versus 110.2 (13.9); p =0.01, mean difference 9.2 (95% CI 2.3 to 16.1)). The nocturnal reduction i n blood pressure ("dipping") was smaller in patients with OSA than in contr ol subjects. Conclusions-Compared with closely matched control subjects, patients with O SA have increased ambulatory diastolic blood pressure during both day and n ight, and increased systolic blood pressure at night. The magnitude of thes e differences is sufficient to carry an increased risk of cardiovascular mo rbidity. The slight excess of upper body fat deposition in the controls mag : make these results conservative.